In recent years, according to heightening of output from engines of automobiles, belt type non-stage transmissions should cope with such requirements. The belt type non-stage transmission is constituted so that a V belt, obtained by connecting a plurality of elements by a belt, is wound around a pair of pulleys which have a groove with a V-shaped cross section and in which the width of the groove can be changed. The belt type non-stage transmission transmits a motive power from a driving pulley to a driven pulley due to a frictional force between the pulleys and the elements. According to the heightening of output in recent years, a clamping force between the pulleys and the elements increases. As a result, wear is generated on contacting surfaces between the pulleys and the elements, and the frictional coefficient therebetween reduces so that traveling performance is possibly deteriorated. For this reason, conventionally, the frictional coefficient on the contacting surfaces between the pulleys and the elements has been heightened, so that the clamping force is reduced, in order to cope with the heightening of output. Further, the frictional coefficient between the pulleys and the elements should be heightened, and wear should be reduced. In order to satisfy both of them, there has been conventionally various developments.
For example, Japanese Patent Application Laid-Open No. 2001-65651 discloses a belt type non-stage transmission in which a portion on a low side of speed ratio, to which transmit a strong motive power of the pulleys, is subject to shot peening so that the frictional coefficient is increased and the wear resistance is improved. It is also disclosed that except for the shot peening, WPC process, plating, coating, grinding and heat treatment may be performed.
Japanese Patent Application Laid-Open No. 2004-144110 discloses a belt type non-stage transmission in which contacting surfaces between the elements and the pulleys are coated with resin containing self-lubricating agent such as graphite, molybdenum disulfide so that the frictional coefficient is heightened and wear resistance is improved.
In the technique exemplified in Japanese Patent Application Laid-Open No. 2001-65651, however, the frictional coefficient and the wear resistance are improved due to a change in surface property caused by shot peening or the like, but its effect turns out to greatly depend on the performance of additive agent in the lubricant. In the above technique, therefore, when the lubricant is deteriorated due to long-time running, a desired performance cannot be obtained, and thus this is insufficient as the improvement of the belt type non-stage transmission. The improvement using the coating disclosed in Japanese Patent Application Laid-Open No. 2001-65651 has a disadvantage that when a film thickness is decreased, the film wears out early, and when the thickness is increased, it is easily peeled off.
A groove with depth of about 40 μm for retaining the lubricant is formed on the contacting surfaces between the pulleys and the elements, but since the contacting surfaces between the elements and pulleys are coated with resin in the technique in Japanese Patent Application Laid-Open No. 2004-144110, it is difficult to accurately fabricate such fine grooves on the resin. For this reason, the retention of the lubricant in the groove becomes insufficient, and a reaction film with the lubricant component is not formed on the contacting surface of the elements, thereby possibly causing seizing. Since heat expansion coefficients are different between the elements and the resin, there is a fear that the resin is peeled off. Further, since the elements are used in the lubricant, there is a fear that the resin is deteriorated and cured due to the lubricant component. The technique of the Japanese Patent Application Laid-Open No. 2004-144110 lacks reliability, which is a serious problem.